Ionomer cements are known. Conventional ionomer cements generally contain a powder component containing aluminosilicate, and a liquid portion usually containing a polymer comprising acidic groups such as polyacrylic acid, polymaleic acid, polyitaconic acid, or a copolymer of at least two of these acids, cf. “New Aspects of the Setting of Glass-ionomer Cements,” Wasson et al., Journal of Dental Research; Vol. 72, No. 2, February, 1993; pages 481-483. The most common polymers comprising acidic groups are derived from polyacrylic acid or copolymers of acrylic and itaconic acid (S. Crisp), acrylic acid and maleic acid,
In glass ionomer cements, the primary reactions which cause the glass ionomer cement to harden is crosslinking based on ionic forces by metal ions released from the glass of polymer comprising acidic groups. Moreover, the acids of the glass ionomer cement partially dilute metal cations from the glass structure during setting so that ionic carboxylates of metal cations may be formed during the setting process.
Dental ionomer cements are characterized by good adhesion properties to enamel and dentin, and the possibility for anticariogenic properties due to the release of fluoride from a fluoride containing glass filler. Moreover, generic cements have a number of further important advantages for applications in dentistry such as the virtual absence of an exothermic reaction, no shrinkage during setting, no free monomer in the set composition, and high dimensional stability. Accordingly, ionomer cements are widely used in the dental field for filling of a cavity, cementing of crowns, inlays, bridges, or orthodontic bands, lining of a cavity, sealing of a root canal, core construction, and preventive sealing.
However, the mechanical properties of glass ionomer cements are usually problematic since glass ionomer materials are inherently brittle. Therefore, the main limitation of the glass ionomer cements is their relative lack of strength and low resistance to abrasion and wear. Conventional glass ionomer cements have low flexural strength but high modulus of elasticity, and are therefore prone to bulk fracture. Further they exhibit rather poor optical properties.
Therefore, the restorative application of ionomer cements in posterior teeth is usually limited to non-stress bearing areas. Ionomer cement materials continue to have significant limitations for use in permanent posterior restorations, particularly with regard to large restorations.
In order to improve the mechanical properties especially flexural strength and fracture toughness, numerous investigation were carried out, such as the use of amino acid modified polymers (Z. Ouyang, S. K. Sneckberger, E. C. Kao, B. M. Culbertson, P. W. Jagodzinski, Appl. Spectros 53 (1999) 297-301; B. M. Culbertson, D. Xie, A. Thakur, J. Macromol. Sci. Pure Appl. Chem. A 36 (1999) 681-96), application of water soluble copolymers using poly(N-vinylpyrrolidone) (D. Xie, B. M. Culbertson, G. J. Wang, J. Macromol. Sci. Pure Appl. Chem. A 35 (1998) 54761), use of polyacids with narrow molecular weight distribution (DE 100 58 829) and branched polyacids (DE 100 58 830). Further polyacids having a limited molecular mass ranging from 20,000 to 50,000 Da (EP 0 797 975) and 1,000 to 50,000 Da (WO 02/41845) were proposed. A further approach was the application of spherical ionomer particles (WO 00/05182).
Resin-modified glass-ionomer cements were introduced with an aim of overcoming the problems associated with the tendency towards brittle fracture of conventional glass-ionomer, while still retaining advantages such as fluoride release and adhesion (EP 0323120, U.S. Pat. No. 4,872,936 and U.S. Pat. No. 5,154,762). Accordingly, it was suggested to replace some of the water in a conventional glass-ionomer cement with a hydrophilic monomer or to modify the polymeric acid so that some of the acid groups were replaced with polymerisable moieties, so that the polymeric acid could also take part in a polymerisation reaction.
Moreover, in order to address the problem of improving the mechanical properties of ionomer cement materials, U.S. Pat. No. 5,369,142 suggests the use of a specific acidic component, namely copolymers of acryloyl or methacryloyl derivatives of amino acids with acrylic acid or methacrylic acid. WO-A 02/062861 discloses polymer compositions for use in glass ionomer dental restoratives having improved resistance to bending and resistance to twisting, whereby the polymers are formed from at least two specific polymers. WO-A 03/061606 discloses ionomer cements containing amino acids improving the mechanical properties.
Polycondensates or heteropolycondensates based an condensable monomer compounds of silicon were described (U.S. Pat. No. 6,124,491) having a straight or branched organic chain of 4 to 50 carbon atoms and at least one double bond.
Thiolated polymers having self-crosslinking properties and their mucoadhesive properties are disclosed in Marschutz. M. K.: Bernkop-Schnurch A. European Journal of Pharmaceutical Sciences 15 (2002) 387-394.